1. Field of the Invention
The present invention relates to a battery-state monitoring system for monitoring the states of battery modules, which is adaptable for a battery system using a battery group having a plurality of battery modules.
2. Description of the Related Art
There is known a battery system using a battery group which consists of a plurality of battery modules connected in series or parallel fashion. An example of the battery system is a battery system for an electric vehicle. It is feared that a reliability of the system is deteriorated when the battery capacities, voltages and temperatures of the battery modules vary in their values. As a result, it is necessary to detect the current states of each battery module on its capacity, voltages and temperature, and to check whether or not the states of the battery modules are correct. Thus, a battery-state monitoring system is used for monitoring the current states of the battery modules.
In an example of the battery-state monitoring system, sensors are respectively provided for the battery modules to detect the current states of those modules, and are electrically connected to a management unit by signal lines. The management unit processes signals received from the sensors, and checks whether or not the current states of the battery modules are correct.
In the thus constructed battery-state monitoring system, a number of sensors are provided while being respectively associated with the battery modules, and connected to the management unit via signal lines. Therefore, a great number of the signal lines are required for their connection, and the wiring of the system is complicated. The wiring complexity leads to deterioration of the system reliability.
On the other hand, the system for monitoring battery states may be arranged such that battery-state monitoring units are respectively provided for the battery modules, and those units are connected to a management unit by two signal lines. In the battery-state monitoring system, communication on the units, are performed between the battery-state monitoring units and the management unit by use of a specific communication protocol. This monitoring system indeed succeeds in considerably simplifying the system wiring; however, it presents another problem. A control for controlling the data communication between the battery-state monitoring units and the management unit is indispensable to the monitoring system. The communication control is comparable with a LAN, and very complicated.